32 BACTERIA IN RELATION TO PLANT DISEASES. 



while the saprophytes are rapid growers. The latter are particularly perplexing and 

 deceptive when through weakness or death of parts they rapidly invade the deeper tissues 

 where the student expects to find only the parasite. If, also, there is some antagonism 

 between the two, then the surface organism may gain complete ascendency in particular 

 portions of the tissue and the cause of the disease may disappear altogether, or appear so 

 sparingly on the plate-cultures that it is entirely overlooked. Literature bristles with 

 examples, the olive-tubercle being a good recent case. Yellow and white non-pathogenic 

 bacteria occur very frequently in olive-knots and on plate-cultures these come up sooner 

 than the parasite. I learned this long ago and Petri, in Rome, has confirmed it recently. 

 Ignorance of this fact led one of the Italian workers to spend two years in carefully working 

 out the biology of the wrong organism a potato bacillus. 



An experiment station bulletin on the bacterial spot of the carnation was based wholly 

 on the wrong organism, a common surface-growing yellow form. The true parasite is a 

 white organism making a quite different type of spot from the one described and figured. 

 This mistake was due to the same cause as the preceding, i. e., improperly controlled 

 inoculation experiments. 



Yellow saprophytic organisms, in particular, are very common on the surface of plants. 

 Mr. Waite found a yellow non-parasitic Schizomycete associated quite frequently with the 

 pear-blight organism, and this misled him for a time. Dr. Arthur must also have had it 

 in some of his cultures for in one place he describes the growth of Bacillus amylovorus as yel- 

 lowish. Chester has described this white organism as pink. 



The writer found yellow non-pathogenic bacteria associated with the yellow Bacterium 

 mahaceamm on the cotton-plant. In 1908 he obtained a whole series of yellow bacteria 

 from the surface of corn kernels, but not Bact. stewarti, which is also yellow, and in many 

 respects like those which were obtained. This corn was undoubtedly infected with Bact. 

 stewarti, but in such small numbers as to evade detection by this method. 



In crown-gall of peach the writer has frequently found non-parasitic yellow and white 

 bacteria, sometimes to the exclusion of the right organism. Yellow ones were also plated 

 out by O'Gara and inoculated without result. Hedgcock also plated out yellow colonies 

 and inoculated unsuccessfully. The same fact has been observed by the writer in daisy 

 gall, in the rose gall, and in rogna of the grape. Once I obtained a nonpathogenic white 

 organism from rogna of grape, once also a non-pathogenic white organism from hard gall of 

 the apple, and later a pathogenic one. These yellow bacteria are so common it must be 

 assumed that they have a special aptitude for the decaying tissues of these plants. 



In old flabby tumors on the hop sent on from California in February the writer found 

 the deeper tissues swarming with green fluorescent and other non-pathogenic Schizomycetes 

 which must have penetrated from the surface of the plant. The right organism was recovered, 

 but it formed only a very small portion of the total bacterial flora of the tumor. Before 

 cutting into it, the surface of this tumor, which was free from distinct fissures, was scraped, 

 washed, plunged into alcohol and then for six minutes in i : r ,000 mercuric chloride water 

 so that contamination by organisms lying on the surface was presumed to have been excluded. 



The writer has seen potatoes typically rotted by Bacillus phytophthorus from which, 

 nevertheless, it was almost impossible to isolate the parasite, its place having been taken by 

 incalculable numbers of nonparasitic, rod-shaped bacteria, which further disintegrated the 

 tissues. In one instance repeated platings from rotting tubers failed, but the right organism 

 was finally obtained indirectly by making a copious inoculation of the diseased flesh into a 

 sound potato, and plating from the latter after decay began. Appel reports a micrococcus 

 as frequently following Bacillus phytophthorus, and this is probably what led Dr. Frank 

 astray. A white non-pathogenic coccus sometimes follows B. tracheiphilus in cucurbit stems. 



Greig Smith has isolated a red micro-organism from sugar-cane attacked by Cobb's 

 disease, and has ascribed the red strands to it. The writer found only yellow bacteria in 

 the red strands. 



